So, I've decided to unearth a very old project of mine: an effects switcher for my guitar rig. Some 10yrs ago I wanted to do this with SSRs, but in the meantime I gave up on that idea and gravitated back to regular low-signal relays.
This will be a rack unit next to my effect pedals and will contain 10 effect loop modules, a power supply and an Arduino to control everything, from MIDI input. The modules themselves will be connected in series in groups of 4 or 5, so I can have some of them before the guitar amp and others in the amp's effects loop.
Now, I've finished a first version of the loop module and I'd appreciate some feedback on it. Relay NO is bypassing the pedal loop, while closed will feed the signal through the pedal.
PS: I know the diode setup across the coil is a bit overkill, but I'm not building this to cost, so it doesn't hurt to have the switch off time shorter, if only for bragging rights.
This will be a rack unit next to my effect pedals and will contain 10 effect loop modules, a power supply and an Arduino to control everything, from MIDI input. The modules themselves will be connected in series in groups of 4 or 5, so I can have some of them before the guitar amp and others in the amp's effects loop.
Now, I've finished a first version of the loop module and I'd appreciate some feedback on it. Relay NO is bypassing the pedal loop, while closed will feed the signal through the pedal.
PS: I know the diode setup across the coil is a bit overkill, but I'm not building this to cost, so it doesn't hurt to have the switch off time shorter, if only for bragging rights.
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As far as I see you could omit the relay k1 and just switch the output from "direct" to "effect" with k2.
Also you probably don't need zener diodes. A flyback diode should be enough.
Edit: just realized that you probably just have the unamplified guitar signal at input. If so it makes sense to disconnect the weak guitar signal from the input resistor of unused effects. Alternatively you could buffer or amplify the guitar input.
Also you probably don't need zener diodes. A flyback diode should be enough.
Edit: just realized that you probably just have the unamplified guitar signal at input. If so it makes sense to disconnect the weak guitar signal from the input resistor of unused effects. Alternatively you could buffer or amplify the guitar input.
Thanks for having a look @stv!
It would, yes, but this setup makes the turn off quicker, which is probably not something I'll ever sense, but for a few extra bucks, why not?
Correct! A buffer would be an option, but it also changes the tone ever so slightly, so I'd avoid that. A device doing exactly what I want is around €1200, so I have enough headroom in my build to use 2x relays
why not just use simple flyback diodes without zeners then? The zeners are useless or even make switching speed worse. Or do I miss something?
Also there is something odd with relay diode D3 connected to the output.
Did part of my research here (see section 4 for the relevant info). Flyback is the slowest, followed by flyback + resistor and then flyback + zener. If I'm understanding the logic correctly, just using a flyback will remove the back EMF but dissipating that energy takes awhile, while the resistor/zener creates a bigger voltage drop so it's faster.
Damn, good catch! Definitely wasn't supposed to be connected to the output, but across the coil just like D4 for K2. I've updated my schematic.
In the meantime I've also developed 2 versions of the PCB for this... one classic and one with "flex cuts" designed to separate the relays on a sort of peninsula which would sit on an elastic (neoprene like) support to dampen vibrations in the hope that it would reduce the mechanical noise.
Routing was obviously a big issue on the flex version and I'm not sure it's worth it, TBH. Curious on what you guys think.
Routing was obviously a big issue on the flex version and I'm not sure it's worth it, TBH. Curious on what you guys think.
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That would be the idea, yes. Why do you think this would be counterproductive? I'm thinking that having a dampening material underneath the tongue, keeping it in tension would dampen vibrations right there on the spot, instead of having them extend towards the rest of the PCB.
I'll check the price estimations on a 4 layer board. Might be a good suggestion to keep routing cleaner
Agreed, if left without a dampener it would act as a tuning fork, but I think it would be better than a classic PCB if one would be added. However, I've looked at the prices of my local fab house for a 4-layer board and it's 3X more expensive.
I'm going to sleep on this. Most probably it's not worth the effort to do the cuts.
I'm going to sleep on this. Most probably it's not worth the effort to do the cuts.
Slept on this a bit and decided the flex cuts are indeed overkill. I can go a simpler route and just mount the relay PCBs with 2 screws on one side and leave the rest hanging. Ringing would be dampened by a dense foam underneath the PCB, while also allowing for proper support.
I've also designed the rest of the boards (power supply, carrier board for an RPI2040 that will do handle the switching logic and an LED indicator board). The power board will use both secondaries from the transformer to allow for less current on regulator/caps, since I had the board space anyway. It also outputs 9V AC that works as "phantom power" through the MIDI cable to power up my Ground Control.
Any thoughts/feedback is welcomed.
I've also designed the rest of the boards (power supply, carrier board for an RPI2040 that will do handle the switching logic and an LED indicator board). The power board will use both secondaries from the transformer to allow for less current on regulator/caps, since I had the board space anyway. It also outputs 9V AC that works as "phantom power" through the MIDI cable to power up my Ground Control.
Any thoughts/feedback is welcomed.
